Ok so i'am writting this code for an exercise we have to write a class for matrices and then to check it we use a code that the teacher wrote to check if it performes the normal operations.
And i don't get exactly where i am wrong it seems to bother the compiler that i return a type Matrix but really i dont get what is a lvalue or rvalue .
But i get this when i try to compile
anthony#anthony-linux:~/Documents/CS/Ex6$ g++ -Wall simplematrixtest.cc Matrix.cc -o simplematrixtest
simplematrixtest.cc: In function ‘int main()’:
simplematrixtest.cc:70:24: error: cannot bind non-const lvalue reference of type ‘Matrix&’ to an rvalue of type ‘Matrix’
70 | Matrix g = f.multiply(a);
| ~~~~~~~~~~^~~
In file included from simplematrixtest.cc:4:
Matrix.hh:13:18: note: initializing argument 1 of ‘Matrix::Matrix(Matrix&)’
13 | Matrix(Matrix &m);
| ~~~~~~~~^
this is my class Matrix:
#include "Matrix.hh"
#include <cmath>
#include <iostream>
using namespace std;
// Default constructor: initializes the Matrix.
Matrix::Matrix() {
nrows=0;
ncols=0;
values=0;
}
// Initializes the Matrix with rows and cols.
Matrix::Matrix(int numberOfRows,int numberOfCols) {
nrows=numberOfRows;
ncols=numberOfCols;
values = new double[nrows*ncols] ;
for (int i = 0; i < nrows*ncols; i++) {
values[i] = 0;
}
}
// Copy constructor
Matrix::Matrix(Matrix &m)
{
nrows=m.getRows();
ncols=m.getCols();
int sizeOfM=m.getRows()*m.getCols();
values = new double[sizeOfM];
for (int i = 0; i < sizeOfM; ++i) {
values[i] = m.values[i];
}
}
// Destructor - Matrix allocates no dynamic resources.
Matrix::~Matrix() {
delete[] values;
// no-op
}
// Mutators:
void Matrix::setElem(int rowIndex,int colIndex,double val){
values[rowIndex*ncols+colIndex]=val; /*See Jasper i listen to what you say ! No return for a void function :) */
}
void Matrix::subtract(Matrix &m) {
for (int i = 0; i < nrows*ncols; i++) {
values[i] -=m.values[i];
}
}
void Matrix::add(Matrix &m) {
for (int i = 0; i < nrows*ncols; i++) {
values[i] +=m.values[i];
}
}
Matrix Matrix::multiply(Matrix &m) {
if(ncols!=m.getRows()){
cout << " Error :invalid matrix multiplication"<< endl;
Matrix ret(0,0);
return ret;
}
else{
Matrix ret(nrows,m.getCols());
for (int rowIndex = 0; rowIndex < ret.nrows; rowIndex++) {
for (int colIndex = 0; colIndex < ret.ncols; colIndex++) {
for(int count=0; count <= ncols; count++) {
ret.values[rowIndex*ncols+colIndex] +=(values[rowIndex*ncols+(count)]*m.values[count*ncols+colIndex]);
}
}
}
return ret;
}
}
// Accessors:
int Matrix::getRows() {
return nrows;
}
int Matrix::getCols() {
return ncols;
}
double Matrix::getElem(int rowIndex,int colIndex){
return values[rowIndex*ncols+colIndex];
}
bool Matrix::equals(Matrix &m) {
if(m.getRows()!=nrows||m.getCols()!=ncols){return false;}
for (int i = 0; i < nrows*ncols; i++) {
if(values[i] !=m.values[i]){return false;}
}
return true;
}
Apparently the problem is in multiply here is the test code
#include <iostream>
using namespace std;
#include "Matrix.hh"
// Have some fun playing with a Matrix!
int main(void) {
// Create a new matrix with two rows and three columns
Matrix a(2, 3);
// Print out some information about the size of this matrix:
cout << "Matrix a is " << a.getRows() << " rows tall." << endl;
cout << "Matrix a is " << a.getCols() << " columns wide." << endl;
// Print out the contents of this matrix (should be all zeroes!):
for(int r = 0; r < a.getRows(); r++) {
for(int c = 0; c < a.getCols(); c++) {
cout << "Element (" << r << ", " << c << ") = " << a.getElem(r,c) << endl;
}
}
// Fill in a few values
a.setElem(1, 2, -5280); // bottom right element is now -5280
a.setElem(0, 1, 123); // top center element is now 123
// Create an identical copy of this matrix
Matrix b = a;
// Change the original matrix some more
a.setElem(1, 2, 555); // bottom right element is now 555
// Examine some elements of each matrix
cout << "(1,2) of a = " << a.getElem(1,2) << " [should be 555]" << endl;
cout << "(1,2) of b = " << b.getElem(1,2) << " [should be -5280]" << endl;
// So if a and b are different, let's copy a into a new matrix and add b to it:
Matrix c = a;
c.add(b);
// Now let's copy c into another new matrix, d, and subtract a from it:
Matrix d = c;
d.subtract(a);
// Hmm... that means d should be b, no?
if (d.equals(b)) {
cout << "Yay! d = b!" << endl;
} else {
cout << "Uh-oh! Something went wrong, d isn't b!" << endl;
}
// Let's create a tiny 0 by 0 matrix using the default constructor:
Matrix e;
cout << "0x0 matrix e is " << e.getRows() << " by " << e.getCols() << endl;
// Of course, e and d are different, since they have different sizes!
if(!e.equals(d)) {
cout << "e and d are indeed different!" << endl;
} else {
cout << "Oh well, back to the drawing board...." << endl;
}
Matrix f(2,2);
f.setElem(0, 0, 2.0);
f.setElem(1, 0, 3.0);
f.setElem(0, 1, 5.0);
f.setElem(1, 1, 7.0);
Matrix g = f.multiply(a);
if (g.getElem(1, 2) == 3885.0) {
cout << "Multiply seems to work!" << endl;
} else {
cout << "Error in multiply() !" << endl;
}
// Okay, enough of this; destroy all those matrices and end the program:
return 0;
}
If i write
Matrix g = a ;
f.multiply(a);
The code compiles without any problem so it is a problem with this line: Matrix g =f.multiply(a);
It is a very simple program and I have just started learning c++ but the for loop is not working in this program. can anyone tell me why the for loop in this c++ program is not running?
#include <iostream>
#include <string>
using namespace std;
class PrimeNo
{
int a;
int c;
public:
// function to check prime number
void chk_Prime(void)
{
cout << "Enter the number: " << endl;
cin >> a;
c=a/2; // to store the condition
for (int i = 2; i < c; ++i)
{
if (a == 0 || a == 1)
{
cout << "The number is not a prime number" << endl;
break;
}
else if (a % i == 0)
{
cout << "This number is not a prime number" << endl;
break;
}
else //if upper conditions are false a number is a prime number
{
cout << "This number is a prime number" << endl;
break;
}
}
}
};
int main()
{
PrimeNo Num;
Num.chk_Prime();
return 0;
}
My Compiler gives runtime error when I initialize the float array in Veccreator function. I am here posting just a sample of what my code looks like.
#include<iostream>
using namespace std;
#define SIZE 1000
class Vector
{
private:
float vecarray[SIZE];
public:
void VecCreator(int dimension)
{
vecarray[SIZE]= { 0 };
cout << "Enter " << dimension << " digits" << endl;
for (int i = 0; i < dimension; i++)
{
cin >> vecarray[i];
}
}
};
int main(void) {
Vector obh;
obh.VecCreator(2);
}
But it works fine with this:`
#include<iostream>
using namespace std;
#define SIZE 1000
class Vector
{
private:
float vecarray[SIZE]= {0};
public:
void VecCreator(int dimension)
{
cout << "Enter " << dimension << " digits" << endl;
for (int i = 0; i < dimension; i++)
{
cin >> vecarray[i];
}
}
};
int main(void) {
Vector obh;
obh.VecCreator(2);
}
Please tell me why the first code is giving error.
Look at the second answer here:
https://social.msdn.microsoft.com/Forums/vstudio/en-US/14e7318e-6fff-4d68-a823-9cbe7b7bc20a/debugging-runtime-check-failure-2-stack-around-the-variable-loggerthread-was-corrupted?forum=vcgeneral
why not do it like here below? i mean if you want to put values in there, why initially put 0 in there?
private:
float vecarray[SIZE];
public:
void VecCreator(int dimension)
{
cout << "Enter " << dimension << " digits" << endl;
for (int i = 0; i < dimension; i++)
{
cin >> vecarray[i];
}
}
now I'm Having problem in repeating the loop after it finished doing the first and i want to try it again without exiting the program? I've been using while loop to do it but still no joy. so i decided to do the if statement. But the Array only accept 4 strings then it exit. Any one who can help? TIA.
#include "stdafx.h"
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
using namespace std;
template <typename T>
void GetContents(T& Input);
template <typename T>
void DisplayContents(const T& Input);
int main()
{
int PASS = 0;
// To Display the unsorted and sorted Book Titles
std::vector<std::string> books;
GetContents(books);
std::cout << "\nMy original library (number of books: " << books.size() << "):\n\n";
DisplayContents(books);
std::sort(books.begin(), books.end());
std::cout << "\nMy sorted library (number of books: " << books.size() << "):\n\n";
DisplayContents(books);
std::cout << "Press 1 to try again, else to quit: ";
std::cin >> PASS;
std::cout << "\n";
if (PASS == 1)
{
GetContents(books);
}
else
{
return 0;
}
// to input All book titles
template <typename T>
void GetContents(T& Input)
{
const int MAX = 5;
string bookName;
std::cout << "Enter a Book Titles:\n> ";
for (int i = 0; i < MAX; i++)
{
std::getline(std::cin, bookName);
Input.push_back(bookName);
std::cout <<">";
}
}
//Display All input book titles
template <typename T>
void DisplayContents(const T& Input)
{
for (auto iElement : Input)
{
std::cout << iElement << '\n';
}
std::cout << '\n';
system("pause");
}
//Purpose: Display first 'n' (user chosen) number if emirps to the console, five per line.
//Note: An "emirp" is a prime number that is also prime when reversed.
#include <iostream>
using namespace std;
bool isPrime(int value); //Prototyle for "prime number function"
int reverse (int value2); //Prototype for "emirp function"
int main()
{
//Ask the user for a positive number
cout << "Please enter a positive number: ";
int n;
cin >> n;
//Reject negative value input
if ( n < 1)
{
cout << "INVALID NUMBER \n";
}
else
{
//Calculate all emirps up to 'n'.
int test = 0;
int number = 2;
while (test < n)
{
if (isPrime(number) && reverse(number))
{
cout << "\n" << reverse(number) << "\t\t\t";
test++;
}
else
{
test++;
}
}
}
system("pause");
return 0;
}
bool isPrime(int value)
{
//If value is prime, the remainder (count) will be zero twice--for 1 and itself.
int divisor = 1;
int count = 0;
int prime = 0;
if (value % divisor == 0)
{
count++;
++divisor;
}
if (count = 2)
{
return true;
}
else
{
return false;
}
}
int reverse(int value2)
{
//reverse the number
value2*=10;
value2 = value2 %10;
value2/=10;
//same procedure as prime function
int divisor2 = 1;
int count2 = 0;
int emirp = 0;
if (value2 % divisor2 == 0)
{
count2++;
++divisor2;
}
if (count2 = 2)
{
int emirp = value2;
}
return emirp;
}
How does this even build?
if (count = 2)
{
...
}
Also:
your reverse function just returns an int, what do you expect
if (isPrime(number) && reverse(number)) to do with that result?
It's not a good way of working to do the whole calculation again btw:
cout << "\n" << reverse(number) << "\t\t\t"; //you already did this in your "check"
Edit:
And no wonder it doesn't work.
You check the number-value (2) every time, not n
If it is just about viewing the console output :
Press CTRL+F5 to run application in Visual studio.
just provide a getch()in main() function
And your code syntax is not in a right way :
if (count = 2) //count ==2
{
return true;
}
if (isPrime(number) && reverse(number))
{
cout << "\n" << reverse(number) << "\t\t\t";
test++;
}
will call reverse() 2 times.
modify it something like ;
int RevNum = reverse(number);
if (isPrime(number) &&RevNum)
{
cout << "\n" << RevNum << "\t\t\t";
test++;
}